Common rail fuel systems are well known and widely used in modern internal combustion engines. In general, a pressurized fluid is supplied to a common rail, having a plurality of fuel injectors fluidly connected therewith. High pressure fluid from the common rail may be used to actuate the injectors, for injecting a fuel into engine cylinders. The pressurized fluid within the rail may be fuel, which not only actuates the injectors but is also injected into the associated cylinders, or the fluid in the rail may be an actuation fluid separate from the fuel which is injected. In many applications, common rail systems tend to offer superior control and efficiency over strategies which rely on individual pumps associated one with each of the fuel injectors.
Over the years, many improvements in fuel system design and operation have relied at least in part upon the ability to inject a fuel into engine cylinders at increasingly higher pressures. Higher pressures in the rail tend to enable higher injection pressures and also relatively precise control over injection initiation and cessation, and improved fuel atomization. A shortcoming of increasing rail pressure, however, is the additional energy required to pressurize the actuation fluid which is supplied to the common rail. Furthermore, pumps and other system components may work at less than optimal efficiency, and can even wear more quickly, when operated to provide relatively high fluid pressures. Further still, the higher the system pressure, the higher the noise created during operation and typically the higher the resulting drive torque fluctuation. Thus, there is ample room for improvement over traditional common rail designs, particularly as the required system pressure thresholds are pushed ever higher.
U.S. Pat. No. 6,786,205 to Stuhldreher et al. sets forth one common rail strategy wherein fluid for the rail is pressurized with hydraulic intensifiers positioned between a fluid supply and the common rail. Stuhldreher et al. purportedly can substitute for systems wherein hydraulic intensification is carried out within each individual fuel injector, reducing the number of parts. While this might be the case in certain instances, Stuhldreher actually increases system complexity at different locations, namely, requiring a relatively complex system of control valves for the intensification units.